The present invention relates generally to a discharge lamp lighting device and more particularly, to a discharge lamp lighting device provided with a failure diagnostic circuit for diagnosing failure of a discharge lamp and a lighting circuit.
There is known a discharge lamp lighting device constructed so that when a discharge lamp cannot be started within a predetermined period of time, it is judged that lighting thereof is impossible, stopping power supply to the discharge lamp (see, for example, JP-U 3-118595).
FIG. 11 shows a constitution of a discharge lamp lighting device of this type. With a light switch 2 turned on, a step-up circuit 1 increases voltage of a battery 3 to output high DC voltage. An inverter 4 converts DC voltage output from the step-up circuit 1 into AC voltage which is applied to a discharge lamp 5 for lighting same. A starter circuit 6 generates high voltage pulses during a predetermined period of time after turning on the light switch 2, which is applied to the discharge lamp 5 for starting same. When supplying power of the battery 3 through the light switch 2, a control circuit 7 controls the step-up circuit 1, the inverter 4, and the starter circuit 6 so as to carry out lighting control of the discharge lamp 5.
FIG. 12 shows details of an external wiring from the lighting circuit to the discharge lamp and the discharge lamp. A discharge lamp lighting device 10 comprising the step-up circuit 1, the inverter 2, the starter circuit 6, and the control circuit 7 is connected to the discharge lamp 5 through a high voltage cable 8a, a connector 9, and a high voltage cable 8b. The discharge lamp 5 includes an outer tube 5a having a discharge lamp bulb 5b mounted therein.
FIG. 13 is a flowchart showing operation of the known discharge lamp lighting device.
At a step S1, it is determined whether or not the light switch 2 is turned on. If the light switch 2 is turned on, the flow proceeds to a step S2 wherein the step-up circuit 1, the inverter 4, and the starter circuit 6 are actuated to start the discharge lamp 5. At a subsequent step S3, it is determined whether or not the discharge lamp 5 is turned on. If the discharge lamp 5 is turned on, the flow proceeds to a step S4, whereas if not, the flow proceeds to a step S7. At the step S4, the step-up circuit 1 and the inverter 4 are controlled to obtain stable lighting of the discharge lamp 5. Subsequently, at a step S5, it is determined whether or not the light switch 2 is turned off. If the light switch 2 is turned off, the flow proceeds to a step S6, whereas if not, the flow returns to the step S4. At the step S6, operation of the step-up circuit 1 and the inverter 4 is stopped to turn off the discharge lamp 5.
At the step S3, if the discharge lamp 5 is not turned on, the flow proceeds to the step S7 wherein it is determined whether or not a predetermined period of time elapses. If the predetermined period of time elapses, the flow proceeds to a step S8, whereas if not, the flow returns to the step S2. At the step S8, operation of the step-up circuit 1, the inverter 4, and the starter circuit 6 is stopped, then the flow proceeds to a step S9. At the step S9, it is determined whether or not the light switch 2 is turned off. If the light switch 2 is turned off, lighting control of the discharge lamp 5 is finished.
In addition, there are known a lighting device so constructed as to turn off the discharge lamp by detecting breakage of a lens thereof (see, for example, JP-U 2-54657), a lighting device so constructed as to stop power supply thereto if the connector is disconnected (see, for example, JP-U 1847), a lighting device so constructed as to stop power supply thereto if anomaly of output voltage, output current, or the like of the circuit is detected (see, for example, JP-A 3-179694), etc.
With the known discharge lamp lighting devices, however, if the discharge lamp is not turned on, starting operation is repeatedly carried out by applying high voltage pulses during a predetermined period of time. Thus, when lighting of the discharge lamp is not possible due to a presence of some failure of the discharge lamp itself or the lighting device, starting operation coercively repeated may produce even breakage of a normal circuit or device.
Moreover, anomaly of output voltage or output current of the circuit cannot be detected without actually operating the lighting device. However, with a presence of failure of the discharge lamp itself or the external wiring from the lighting device to the discharge lamp, operation of the discharge lamp may produce breakage of a normal circuit or device.
It is, therefore, an object of the present invention to provide a system for and a method of lighting a discharge lamp which enables detection of a circuit or device as malfunctioned without any breakage of a normal circuit or device.